4,319 research outputs found
Striped superconductors in the extended Hubbard model
We present a minimal model of a doped Mott insulator that simultaneously
supports antiferromagnetic stripes and d-wave superconductivity. We explore the
implications for the global phase diagram of the superconducting cuprates. At
the unrestricted mean-field level, the various phases of the cuprates,
including weak and strong pseudogap phases, and two different types of
superconductivity in the underdoped and the overdoped regimes, find a natural
interpretation. We argue that on the underdoped side, the superconductor is
intrinsically inhomogeneous -- striped coexistence of of superconductivity and
magnetism -- and global phase coherence is achieved through Josephson-like
coupling of the superconducting stripes. On the overdoped side, the state is
overall homogeneous and the superconductivity is of the classical BCS type.Comment: 5 pages, 3 eps figures. Effect of t' on stripe filling + new
references are adde
Effect of nonhydrostatic pressure on the superconducting kagome metal CsVSb
High-pressure single-crystal x-ray diffraction experiments reveal that the
superconducting kagome metal CsVSb transforms from hexagonal ()
to monoclinic () symmetry above 10 GPa if nonhydrostatic pressure
conditions are created in a diamond anvil cell with silicon oil as
pressure-transmitting medium. This is contrary to the behavior of CsVSb
under quasi-hydrostatic conditions in neon, with the hexagonal symmetry
retained up to at least 20 GPa. Monoclinic distortion leaves the kagome planes
almost unchanged but deforms honeycomb nets of the Sb atoms. Using ab initio
density-functional calculations, we show that this distortion facilitates the
pressure-induced shift of van Hove singularities away from the Fermi level and
assists in the Fermi surface reconstruction caused by the formation of
interlayer Sb-Sb bonds, thus adding a structural transition component to the
reentrant behavior of CsVSb.Comment: 5 pages, 4 figures, 2 table
Nonlocality of Kohn-Sham exchange-correlation fields in dielectrics
The theory of the macroscopic field appearing in the Kohn-Sham
exchange-correlation potential for dielectric materials, as introduced by
Gonze, Ghosez and Godby, is reexamined. It is shown that this Kohn-Sham field
cannot be determined from a knowledge of the local state of the material (local
crystal potential, electric field, and polarization) alone. Instead, it has an
intrinsically nonlocal dependence on the global electrostatic configuration.
For example, it vanishes in simple transverse configurations of a polarized
dielectric, but not in longitudinal ones.Comment: 4 pages, two-column style with 2 postscript figures embedded. Uses
REVTEX and epsf macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/index.html#dv_gg
Effects of Backflow Correlation in the Three-Dimensional Electron Gas: Quantum Monte Carlo Study
The correlation energy of the homogeneous three-dimensional interacting
electron gas is calculated using the variational and fixed-node diffusion Monte
Carlo methods, with trial functions that include backflow and three-body
correlations. In the high density regime the effects of backflow dominate over
those due to three-body correlations, but the relative importance of the latter
increases as the density decreases. Since the backflow correlations vary the
nodes of the trial function, this leads to improved energies in the fixed-node
diffusion Monte Carlo calculations. The effects are comparable to those found
for the two-dimensional electron gas, leading to much improved variational
energies and fixed-node diffusion energies equal to the release-node energies
of Ceperley and Alder within statistical and systematic errors.Comment: 14 pages, 5 figures, submitted to Physical Review
Boltzmann equation and hydrodynamic fluctuations
We apply the method of invariant manifolds to derive equations of generalized
hydrodynamics from the linearized Boltzmann equation and determine exact
transport coefficients, obeying Green-Kubo formulas. Numerical calculations are
performed in the special case of Maxwell molecules. We investigate, through the
comparison with experimental data and former approaches, the spectrum of
density fluctuations and address the regime of finite Knudsen numbers and
finite frequencies hydrodynamics.Comment: This is a more detailed version of a related paper: I.V. Karlin, M.
Colangeli, M. Kroger, PRL 100 (2008) 214503, arXiv:0801.2932. It contains
comparison between predictions and experiment, in particular. 11 pages, 6
figures, 2 table
Inhibition of IGF1-R overcomes IGFBP7-induced chemotherapy resistance in T-ALL
Background T-cell acute lymphoblastic leukemia (T-ALL) is a genetically
heterogeneous disease with the need for treatment optimization. Previously,
high expression of Insulin-like growth factor binding protein 7 (IGFBP7), a
member of the IGF system, was identified as negative prognostic factor in
adult T-ALL patients. Since aberrant IGFBP7 expression was observed in a
variety of neoplasia and was relevant for prognosis in T-ALL, we investigated
the functional role of IGFBP7 in Jurkat and Molt-4 cells as in vitro models
for T-ALL. Methods Jurkat and Molt-4 cells were stably transfected with an
IGFBP7 over-expression vector or the empty vector as control. Proliferation of
the cells was assessed by WST-1 assays and cell cycle status was measured by
flow-cytometry after BrDU/7-AAD staining. The effect of IGFBP7 over-expression
on sensitivity to cytostatic drugs was determined in AnnexinV/7-AAD assays.
IGF1-R protein expression was measured by Western Blot and flow-cytometric
analysis. IGF1-R associated gene expression profiles were generated from
microarray gene expression data of 86 T-ALL patients from the Microarrays
Innovations in Leukemia (MILE) multicenter study. Results IGFBP7-transfected
Jurkat cells proliferated less, leading to a longer survival in a
nutrient–limited environment. Both IGFBP7-transfected Jurkat and Molt-4 cells
showed an arrest in the G0/G1 cell cycle phase. Furthermore, Jurkat
IGFBP7-transfected cells were resistant to vincristine and asparaginase
treatment. Surface expression and whole protein measurement of IGF1-R protein
expression showed a reduced abundance of the receptor after IGFBP7
transfection in Jurkat cells. Interestingly, combination of the IGF1-R
inhibitor NPV-AEW541 restored sensitivity to vincristine in IGFBP7-transfected
cells. Additionally, IGF1-R associated GEP revealed an up-regulation of
important drivers of T-ALL pathogenesis and regulators of chemo-resistance and
apoptosis such as NOTCH1, BCL-2, PRKCI, and TP53. Conclusion This study
revealed a proliferation inhibiting effect of IGFBP7 by G0/G1 arrest and a
drug resistance-inducing effect of IGFBP7 against vincristine and asparaginase
in T-ALL. These results provide a model for the previously observed
association between high IGFBP7 expression and chemotherapy failure in T-ALL
patients. Since the resistance against vincristine was abolished by IGF1-R
inhibition, IGFBP7 could serve as biomarker for patients who may benefit from
therapies including IGF1-R inhibitors in combination with chemotherapy
Formulation and implementation of decohesion elements in an explicit finite element code
The Coupled Electron-Ion Monte Carlo Method
In these Lecture Notes we review the principles of the Coupled Electron-Ion
Monte Carlo methods and discuss some recent results on metallic hydrogen.Comment: 38 pages, 6 figures, Lecture notes for the International School of
Solid State Physics, 34th course: "Computer Simulation in Condensed Matter:
from Materials to Chemical Biology", 20 July-1 August 2005 Erice (Italy). To
appear in Lecture Notes in Physics (2006
A quantum Monte Carlo study of the one-dimensional ionic Hubbard model
Quantum Monte Carlo methods are used to study a quantum phase transition in a
1D Hubbard model with a staggered ionic potential (D). Using recently
formulated methods, the electronic polarization and localization are determined
directly from the correlated ground state wavefunction and compared to results
of previous work using exact diagonalization and Hartree-Fock. We find that the
model undergoes a thermodynamic transition from a band insulator (BI) to a
broken-symmetry bond ordered (BO) phase as the ratio of U/D is increased. Since
it is known that at D = 0 the usual Hubbard model is a Mott insulator (MI) with
no long-range order, we have searched for a second transition to this state by
(i) increasing U at fixed ionic potential (D) and (ii) decreasing D at fixed U.
We find no transition from the BO to MI state, and we propose that the MI state
in 1D is unstable to bond ordering under the addition of any finite ionic
potential. In real 1D systems the symmetric MI phase is never stable and the
transition is from a symmetric BI phase to a dimerized BO phase, with a
metallic point at the transition
Pressure evolution of electron dynamics in the superconducting kagome metal CsVSb
The coexistence of the charge-density wave (CDW) and superconducting phases
and their tunability under external pressure remains one of the key points in
understanding the electronic structure of VSb ( = K, Rb, Cs)
kagome metals. Here, we employ synchrotron-based infrared spectroscopy assisted
by density-functional calculations to study the pressure evolution of the
electronic structure at room temperature up to 17 GPa experimentally. The
optical spectrum of CsVSb is characterized by the presence of localized
carriers seen as a broad peak at finite frequencies in addition to the
conventional metallic Drude response. The pressure dependence of this
low-energy peak reflects the re-entrant behavior of superconductivity and may
be interpreted in terms of electron-phonon coupling, varying with the growth
and shrinkage of the Fermi surface. Moreover, drastic modifications in the
low-energy interband absorptions are observed upon the suppression of CDW.
These changes are related to the upward shift of the Sb2 band that
eliminates part of the Fermi surface around the -point, whereas band saddle
points do not move significantly. These observations shed new light on the
mixed electronic and lattice origin of the CDW in CsVSb
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